The ability to separate a particle/fluid mixture into its separate components is desirable in many applications. Acoustophoresis is the separation of particles using high intensity sound waves, and without the use of membranes or physical size exclusion filters. It has been known that high intensity standing waves of sound can exert forces on particles in a fluid when there is a differential in both density and compressibility, otherwise known as the contrast factor. A standing wave has a pressure profile which appears to “stand” still in time. The pressure profile in a standing wave contains areas of net zero pressure at its nodes and anti-nodes. Depending on the density and compressibility of the particles, they will be trapped at the nodes or anti-nodes of the standing wave. The higher the frequency of the standing wave, the smaller the particles that can be trapped.
Conventional acoustophoresis devices have had limited efficacy due to several factors including heat generation, limits on fluid flow, and the inability to capture different types of materials. In particular, heat generation can be deleterious to materials in the fluid stream, particularly in biopharmaceutical applications when materials such as Chinese hamster ovary (CHO) cells and proteins and monoclonal antibodies expressed therefrom are present in the fluid stream.
In this regard, an ultrasonic transducer including a piezoelectric element has typically been used to generate ultrasonic waves. The transducer is generally mounted into the wall of a chamber, with a reflector mounted in the opposite wall. The face of the reflector is parallel to the face of the piezoelectric element, maximizing reflection of the incident wave generated from the piezoelectric element to form the standing wave. Heat is generated by the piezoelectric element during operation when performing acoustophoresis. It would be desirable to provide alternative designs that minimize heat generation.